Hi 240ists, long time owner/lurker first time poster (I think).

Anyway I've got this warbling/whirring sound coming from my engine compartment but I can't place exactly where it is. It's intermittent, usually happens most on a cold start. I thought it was a vacuum leak problem because it's almost a whistle and it changes with RPMs. It happens when I'm in park/neutral so I've ruled out the transmission, and it doesn't follow the gears exactly. It sounds like it follows some internal gear shifting mechanism, Anyway I caught a bit of it on video/audio. It's not a great representation because I'm not in motion shifting gears, but it gets the gist of it


it honestly reminds me of the jetsons car sound: (really dating myself there)

you can hear as the RPMs increase so does the pitch. Again when it shifts gear it also changes pitch. I wasn't able to capture that but I can if that'll help diagnose the issue. I thought initially the timing belt roller or tensioner bearing as it seems to be coming from that area. I've got a mechanic's stethoscope and honestly it sounds like it's coming from under the valve cover.

Thanks for any help you can give!

 

Besides the timing belt, check the tension of all belts in the engine compartment. Sometimes, worn-out or misaligned belts can make similar noises, especially during cold starts.
Also, a bad pulley bearing can make a whirring noise, like what you're hearing.
Check all the fluids like engine oil, power steering fluid, and transmission fluid.
And look for leaks or loose parts in the exhaust system that could make unexpected noises in the engine area.

 

good call, I bought all the belts. I have no idea when the previous owner changed them so it’s nice to have that done. I’ve even got the timing belt, which I’ll attempt for the first time to rule it out. I also don’t think it’s been changed.

Occam’s razor says it’s oil level. I changed it recently and the sound started occurring not long after, so that’s the first thing I’m going to do.

thanks again for the tips, I’ll reply here when I have more info.

 

For those with the same problem in the future, I fixed it by changing the timing belt tensioner. It was definitely going and was 99% certainly the source of the sound. However while I was in there I also changed all the V belts, the water pump, the thermostat and housing and did a coolant flush. Running like a top now. Thanks again @Niklas11Braun !